Such cartridge assemblies are known which comprise an elongate chamber containing a fluent substance with an outlet at one end and a piston at the other end. The outlet is commonly defined by an externally screw threaded hollow boss onto which in use a nozzle is screwed and which out of use is closed by a cap screwed onto the boss. In order to expel the fluent substance from the cartridge the piston is pushed towards the front of the cartridge.
With an arrangement of this kind it is not possible to control well the flow of substance from the cartridge.
In order to improve the control of the flow, the dispenser could be provided with a control valve between the cartridge and the nozzle outlet. However, if such a control valve were provided the valve would require cleaning each time the dispenser was used which would be a serious disadvantage to the user.